This concept is directed to a double-acting, two-stage flow control valve (DATS Valve) for use as a hydraulic control device. The present invention has use generally as a hydraulic control device and may be used, for example, in a camless engine. Additionally, the present application is directed specifically at the use of the hydraulic control device in combination with an intensified, low-pressure, common rail fuel injector used in a hydraulically-actuated, electronically-controlled unit injection (HEUI) system for an internal combustion engine, particularly a diesel engine, and the method of operating the control valve to selectively achieve pilot injection, rate shaping injection, far split injection, and single shot injection modes of operation of the fuel injector.
The prior art injectors used here for reference are the hydraulically-actuated, electronically-controlled unit injectors described in the following references, which are incorporated herein by reference: SAE paper No. 930270, xe2x80x9cHEUIxe2x80x94A New Direction for Diesel Fuel Systems,xe2x80x9d and SAE paper No. 1999-01-0196, xe2x80x9cApplication of Digital Valve Technology to Diesel Fuel Injectionxe2x80x9d and U.S. Pat. Nos. 5,271,371, 5,479,901, 5,597,118, and 5,720,261, and 5,720,318.
A prior art HEUI injector 200 is depicted in prior art FIG. 1. HEUI 200 consists of four main components: (1) control valve 202; (2) intensifier 204; (3) nozzle 206; and (4) injector housing 208.
The purpose of the control valve 202 is to initiate and end the injection process. Control valve 202 is comprised of a poppet valve 210, having an attached armature 213, and an electric control solenoid 212. High pressure actuating oil from a high pressure rail 215 is supplied to the lower seat 214 of the poppet valve 210 through oil passageway 216. To begin injection, the electric control solenoid 212 is energized moving the poppet valve 210 upward from the lower seat 214 to the upper seat 218. This action admits high pressure oil to the spring cavity 220 and through the passage 222 to the piston chamber 223 of the intensifier 204. Injection continues until the solenoid of the electric control 212 is de-energized and the poppet 210 moves from the upper seat 218 to lower seat 214. Oil and fuel pressure then decrease as spent oil is ejected from the injector 200 through the open upper seat oil discharge 224 to the valve cover area of the internal combustion engine. The valve cover area is at ambient pressure.
The middle segment of the injector 200 includes the intensifier 204. The intensifier 204 includes the hydraulic intensifier piston 236, the plunger 228, fuel chamber 230, and the plunger return spring 232.
Intensification of the fuel pressure to desired injection pressure levels is accomplished by the ratio of areas between the upper surface 234 of the intensifier piston 236, acted on by the high pressure actuating oil and the lower surface 238 of the plunger 228, acting on the fuel in chamber 230. The intensification ratio can be tailored to achieve desired injection characteristics. Fuel is admitted to chamber 230 through passageway 240 past check valve 242. Injection begins as the high pressure actuating oil is supplied to the upper surface 234 of the intensifier piston 236.
As the intensifier piston 236 and plunger move downward responsive to the force exerted by the actuation oil, the pressure of the fuel in the chamber 230 below the plunger 228 rises dramatically. High pressure fuel flows in passageway 244 past check valve 246 to act upward on needle valve surface 248. The upward force on surface 248 opens needle valve 250 and fuel is discharged from orifice 252 into the combustion chamber of the engine. The intensifier piston 236 continues to move downward until the solenoid of the electric control 212 is de-energized causing the poppet valve 210 to return to the lower seat 214, thereby blocking actuating oil flow. The plunger return spring 232 returns the piston 236 and plunger 228 to their initial upward seated positions. As the plunger 228 returns upward, the plunger 228 draws replenishing fuel into the plunger chamber 230 across ball check valve 242.
The nozzle 206 is typical of other diesel fuel system nozzles. The valve-closed-orifice style is shown, although a mini-sac version of the tip is also available. Fuel is supplied to the nozzle orifice 252 through internal passages. As fuel pressure increases, the nozzle needle 250 lifts from the lower seat 254 to its open position, thereby allowing fuel injection to occur. As fuel pressure decreases at the end of injection, the spring 256 returns the needle 250 to its closed position against the lower seat 254.
FIGS. 2a, 2b, 2c, and 2d illustrate a prior art Digital Hydraulic Operating System (DHOS) injector and digital control valve operation. The intensifier and nozzle portions of the DHOS injector are similar to those of the HEUI injector and have been identified with the same reference numerals. However, in the DHOS injector, the poppet control valve 202 of the HEUI injector has been replaced by a spool type digital control valve 300 which is controlled by two solenoid coils 302, 304, the valve spool 306 which is made of magnetic material, being the armature. Thus, as illustrated in FIG. 2c, when the coil 302 is energized to begin an injection event or engine cycle during which an injection occurs, the valve spool 306 is pulled toward the coil 302 thereby open a fluid connection between the hydraulic fluid (high pressure lube oil) supply passage 310 and the working fluid passages 312 to the intensifier chamber 223 within the injector while isolating the vent passages 314. When the coil 302 is de-energized, the valve spool will remain in the open position shown in FIG. 2c due to residual magnetism in the valve spool 306.
To end the injection, the coil 304 is energized to pull the valve spool 306 rightward toward the coil 304 thereby establishing a fluid connection between the vent passages 314 and the working fluid passages 312 to the intensifier chamber 223 within the injector while isolating the hydraulic fluid supply passage 310.
With either the HEUI or the DHOS injector, the size of the control valve normally is targeted for a single injection operation for achieving maximum injection pressure. And it is also sized for good performance at low temperature operation when hydraulic fluid is relatively viscous. Once the size of the control valve is selected, the fuel delivery quantity may be determined based on the actuation pressure and valve open duration (pulse width duration). The maximum fuel delivery for these type injectors could reach 200 mm3/stroke for full engine load condition. The minimum fuel delivery for engine at idle could be as small as 4 mm3/stroke. Especially for the DHOS injector, the digital valve is also responsible for pilot injection operation. The pilot injection quantity can be as small as 1 mm3/injection at maximum actuation pressure, approximately 3000 psi.
When a large size control valve is used for a small quantity of fuel delivery, significant performance variability is introduced during shot-to-shot and injector-to-injector operation. It is believed that this performance variability can be reduced if a smaller valve is used for small quantity operation and a large valve for full capacity operation.
The present invention is a valve for use generally as a hydraulic control device, such as, for example, in a camless internal combustion engine. One of the specific purposes of this invention is a control valve for a unit fuel injector, which can provide small flow when it is needed and can be switched to provide a larger flow rate when desired. Fundamentally, the control valve of the present invention has the ability to provide two-stage flow (high rate of flow and low rate of flow) with flexible controllability.
Many advanced diesel injector features, such as pilot injection, rate shaping, and efficient single shot injection, have been made available in various forms in prior injectors. All these features need to be available on a single injector for a diesel engine to achieve the goal of meeting ever more stringent emission regulations. With this invention, the user can flexibly choose between pilot injection, rate shaping injection, and single shot injection. The quantity of the fuel delivery and schedule of all events are flexibility selected and controlled.
This invention covers three different concepts. The first is a double-acting two stage (DATS) valve configuration as illustrated in the FIG. 3. The second concept is the combination of a DATS valve with a low pressure, intensified, hydraulically-actuated, electrically-controlled, common rail diesel fuel injector as shown in FIG. 6. The third concept is the operating strategies for the DATS injector to produce various modes of fuel injection as shown in FIG. 7 depending on various engine operating conditions. Although this valve concept can be used in many different applications, the direct application of this particular DATS valve is in diesel engine injection systems.
The present invention is a control valve assembly for use with a fuel injector, the fuel injector being controllable to define selected injection strategy of an injection event and includes a control valve having an inlet port and a drain port, the inlet port being in flow communication with a source of actuating fluid and the drain port being in flow communication with an actuating fluid drain having a first and a second independently shiftable valve member being configurable during an injection event to define a plurality of actuating fluid flow paths for controlling the injection event. The present invention is further a fuel injector that includes the aforementioned control valve. Additionally, the present invention is a method of controlling injection strategy of an injection event of a fuel injector which includes a number of steps, including the step of;
independently controlling the shifting of two valves in the control valve assembly to selectively control the flow of high pressure actuating fluid to the intensifier chamber to effect the desired injection strategy.